The present invention relates, in general, to the production of printed circuit components and, in particular, to an apparatus and a method for compensating for distortions in the size of substrates of printed circuit workpieces by which the functional circuit features that are to be developed on the printed circuit component are expanded or contracted depending upon the nature of the distortion.
It is common practice, in the fabrication of printed circuits, to: (1) project an image of the desired circuit onto a photoresist coating overlaying a metal layer on a substrate, (2) remove the imaged, soluble photoresist in a develop solution, (3) etch away those portions of the metal layer where the resist was removed in the develop process, and (4) remove the remaining photoresist that was used as the etch mask, leaving the desired metal layer circuit on the substrate. The metal layer circuit is often registered to underlying substrate features. Prior to the creation of the imaged metal circuit layer, the substrate might undergo certain process operations that cause change in the character of the substrate, such as it""s size in both length and width.
With the use of certain substrate materials, for example ceramic substrates, these changes in size of the substrate can be predicted and the desired circuit features presented on the mask from which the image of the desired circuit features are projected onto the photoresist coating can be arranged to compensate for such changes in the substrate. With the use of certain other substrate materials, for example teflon, these changes in size of the substrate cannot be predicted with the required repeated accuracy. Therefore, the desired circuit features cannot be arranged to compensate for such changes in the substrate.
It is an objective of the present invention to provide a new and improved apparatus and method for compensating for distortions in the size of substrates of printed circuit workpieces by which the functional circuit features that are to be developed on the printed circuit component are expanded or contracted depending upon the nature of the distortion.
It is another objective of the present invention to provide such an apparatus and method that are accurate and cost effective.
According to the present invention, a mask bearing an image composed of a functional circuit feature and at least two alignment features is provided. Also provided is a table for holding a substrate containing at least one printed circuit workpiece having at least two alignment features. Light from a light source is projected through the mask and a lens to project the mask alignment features onto the table. Also provided are a sensor attached to the table and a camera. The sensor is moved to a position at least approximately at the projection of a first of the mask alignment features and data is developed of the movement of the sensor to a position at least approximately at the projection of the first of the mask alignment features. Next, the sensor is scanned along two orthogonal axes of the table through the projection of the first of the mask alignment features and data is developed of the scan of the sensor along both of the orthogonal axes through the projection of the first of the mask alignment features. Also, data is developed of the intensity of the light detected by the sensor as the sensor is scanned through the projection of the first of the mask alignment features. The sensor then is moved to a position at least approximately at the projection of a second of the mask alignment features and data is developed of the movement of the sensor to a position at least approximately at the projection of the second of the mask alignment features. Next, the sensor is scanned along the two orthogonal axes of the table through the projection of the second of the mask alignment features and data is developed of the scan of the sensor along both of the orthogonal axes through the projection of the second of the mask alignment features. Also, data is developed of the intensity of the light detected by the sensor as the sensor is scanned through the projection of the second of the mask alignment features. The mask is moved rotatably in response to the data of the scans of sensor and data of the light intensities, so that projections of the mask alignment features are on a line parallel to one of the orthogonal axes.
Further in accordance with the present invention, the table moved to position a first of the printed circuit workpiece alignment features into alignment with a camera and data is developed of the movement of the table to move the first of the printed circuit workpiece alignment features into alignment with the camera. The table then is moved to position a second of the printed circuit workpiece alignment features into alignment with the camera and data is developed of the movement of the table to move the second of the printed circuit workpiece alignment features into alignment with the camera. The mask is then moved rotatably in response to the data of the alignments of the printed circuit workpiece alignment features with the camera to adjust the orientation of the functional circuit feature and the lens is then moved vertically in response to the data of the alignments of the printed circuit workpiece alignment features with the camera to adjust the magnification of the functional circuit feature.
Further in accordance with the present invention, the data developed during mask alignment and workpiece alignment is combined to develop alignment offsets that are applied to the final positioning of the printed circuit workpiece under the optical axis of the lens. The light source then illuminates the projected circuit image onto photoresist on the printed circuit workpiece.